Officials in western Ethiopia are investigating the disappearance of the Gambella state governor, who vanished last Friday. His disappearance follows violent ethnic clashes last month that prompted thousands of people to flee the region and seek refuge in Sudan.

Ethiopian government spokesman Zemedkun Teckle says officials in Addis Ababa have no idea what has happened to the governor of Gambella state, Okelo Akuai.

"The reason why he disappeared from that area is not actually clear. What we can say at this point is the reason is under investigation."

Mr. Akuai's four-wheel drive vehicle was found in the state capital, Gambella town, shortly after he was reported missing on Friday. But officials say no one has heard from him or from his missing driver and bodyguards.

International humanitarian and human-rights organizations believe the governor's disappearance may be linked to heightened tension between the Anuak and the Nuer, two tribes among several rival ethnic groups in the remote area, near the border with Sudan.

There are fears Mr. Akuai, who is an Anuak, may have been the victim of an attack. But some humanitarian workers speculate that he may have fled into Sudan.

Anuaks fear they are losing their land to the nomadic Nuer, whose numbers in Gambella have been steadily rising for several decades. The latest fighting erupted in early December, after an attack on a U-N vehicle left eight-people dead. Among them were three government workers who were trying to set up a new refugee camp for thousands of Nuers in territory traditionally held by the Anuak.

A radical Anuak group was immediately blamed for that attack, sparking several days of ethnic clashes, which killed dozens of mostly Anuak people. In response to the unrest, the government sent as many as five-thousand troops to Gambella to restore order.

But an international human-rights organization, Genocide Watch, claims that government troops were actually sent to fuel the fighting, not to stop it.

On its Internet web site, Genocide Watch says it has confirmed numerous reports of massacres of Anuaks, some of them by Ethiopian troops. The organization says nearly 420 Anuaks were murdered last month, prompting thousands of Anuaks to flee into Sudan.

Genocide Watch accuses the Ethiopian government of trying to drive the Anuaks out of Gambella because oil was recently discovered in Anuak territory. The organization compares the situation to the plight of the southern Sudanese across the border.

The Ethiopian government spokesman, Mr. Zemedkun, says such allegations are baseless.